摘要:

Hydrogen passivation of Zn acceptors and Zn–H dissociation kinetics are compared for homoepitaxial and lattice‐mismatched heteroepitaxialn+pInP structures. Doping profile measurements show a pronounced increase in the depth and degree of passivation in thep‐type region of the heteroepitaxial samples indicating enhanced diffusion of hydrogen along dislocations, followed by additional Zn deactivation. Moreover, the strong affinity between hydrogen and extended defects is found to aid the subsequent dissociation of the Zn–H complexes as indicated by (i) reverse bias annealing (RBA) studies which show that the Zn–H dissociation energy decreases from 1.19 eV in homoepitaxial samples to 1.12 eV in heteroepitaxial samples, and (ii) enhanced passivation of extended defect‐related traps by hydrogen that is liberated from Zn acceptors during the RBA process as determined by deep level transient spectroscopy. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117909

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A sampling correlator is described which is useful for characterizing optical pulses with subpicosecond resolution. The correlator exploits the ultrafast nonlinear response of a photoconductor made of low‐temperature‐grown (LTG) gallium arsenide, which is connected to a coplanar‐waveguide line. Instead of using a nonlinear crystal, the LTG‐GaAs correlator uses a nonlinearity associated with the transmission line and photoconductor functioning as a voltage divider. The resulting nonlinearity is used to measure the intensity autocorrelation function. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117910

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have investigated surface morphology of YBa2Cu3O7−ythin films prepared by chemical vapor deposition (CVD) using liquid metalorganic (MO) sources on MgO(100) single crystalline substrates by atomic force microscopy (AFM). An abrupt change in the terrace width was observed at the deposition temperature of around 750 °C. An anomalous decrease in the efficiency of incorporation of the yttrium component into the film was also found above the same temperature. It suggests that the appearance of liquid phase on the growing surface and the growth mode change from the conventional vapor growth to the VLS (vapor–liquid–solid) growth mode at this temperature. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117911

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We analyzed the transport of charge carriers across PrBa2Cu3−xGaxO7−&dgr;(PBCGO) barriers as a function of barrier thickness, Ga‐doping level, temperature, and bias voltage. It was found that by Ga doping, the normal state resistance (Rn) of the junctions was systematically increased, while the critical current (Ic) remained constant. We argue that pair transport takes place by direct tunneling, whereas the quasiparticles have access to channels formed by one or more localized states inside the barrier. By Ga doping theIcRnproducts were increased, up to 8 mV at 4.2 K for junctions with 8 nm thick PrBa2Cu2.6Ga0.4O7−&dgr;barriers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117912

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report measurements of 1/felectrical noise in two hole doped manganite perovskite oxides, La0.67Ca0.33MnO3and Pr0.67Sr0.33MnO3, which exhibit colossal magnetoresistance. The noise magnitude represented by the Hooge parameter is nearly 8 orders of magnitude larger than that observed in ordinary metals (and semiconductors) and nearly 5–6 orders of magnitude larger than that observed in epitaxial films of the perovskite oxide YBa2Cu3O7in the normal state. The normalized noise spectral density increases with decreasing temperature below the resistivity peak, suggestive of the presence of additional low energy noise processes in the ferromagnetic metallic state. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117913

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

High quality Y3Fe5O12/Gd3Ga5O12(YIG/GGG) superlattices have been grown on (111)GGG substrates by pulsed laser deposition. The superlattices are investigated with the thickness of the YIG layer varied from six to one unit cells while keeping the GGG layer fixed at one unit cell. The thicknesses of the YIG and GGG layers are confirmed with grazing angle x‐ray reflectivity (GAXR). The good quality of the samples is indicated by the small interface roughness, no more than 6 A˚, also measured with GAXR. While the magnetization of the samples decreases when the thickness of the YIG layer is decreased, the superlattice remains magnetic even when the YIG layer is only one unit cell. Ferrimagnetic resonance indicates that there exists a surface anisotropy favoring in‐plane magnetization. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117914

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Magnetic thin films have been deposited by molecular beam epitaxy on vicinal Si(111) substrates misoriented towards [11‐2]. The substrates were thermally pretreated in order to activate the step bunching mechanism, which results in a laterally modulated surface topology with a period of ∼800 A˚. Cobalt or permalloy layers grown on such surfaces exhibit an in‐plane uniaxial magnetic anisotropy. This anisotropy is associated with the lateral pseudoperiodic variation of the crystalline orientation of the metallic layers as observed by transmission electron microscopy. Magnetoresistance measurements on microstructured films reveal a single‐domain behavior with a magnetization reversal by rotation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117915

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Patterned thin films of TiO2were deposited from aqueous solution onto photopatterned self‐assembled monolayer (SAM) films on Si substrates. Regions of the SAM containing sulfonate surface functionality were created by the photo‐oxidation of initially deposited thioacetate groups through a mask. The nanocrystalline TiO2‐on‐SAM films were deposited selectively on the photolyzed regions of the SAM. The electrical properties of such films were assessed for potential microelectronic device applications. Current–voltage and capacitance–voltage measurements made on nonpatterned TiO2films yielded values of relative permittivity ranging from 24 to 57, film resistivities of 1.0–1.5×109&OHgr; cm and breakdown voltages in excess of 1 MV/cm. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117916

出版商:AIP    

年代:1996

数据来源: AIP